The Electronic Structure of the FeSe / Ti1+xO2 / SrTiO3 Interface

FeSe / Ti1 xO2 / SrTiO3 界面的电子结构

• 批准号: 2032810
• 负责人: Hunter Sims
• 金额: $ 10.19万
• 依托单位: Francis Marion University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-02-01 至 2023-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2032810&HistoricalAwards=false
• 关键词: Electronic; Structure; FeSe; Ti1+xO2; SrTiO3

The promise of transmitting electricity without loss makes superconductivity at standard temperature and pressure one of the most tantalizing goals in materials science. However, a comprehensive explanation of high-temperature superconductivity remains elusive. To chart a path forward, scientists must study individual materials to try to understand how they work and what they have in common. This project will provide computational tools for the study of how superconducting materials react to changes in their atomic structure. Understanding these changes allows researchers to predict ways to increase the operating temperature of a superconducting material, allowing experiments to focus on the most promising candidates. These tools will be applied to the case of iron selenide (FeSe) deposited on strontium titanate (SrTiO3). A single three-atom-thick layer of FeSe grown on SrTiO3 remains superconducting up to temperatures almost 10 times greater than larger crystals of pure FeSe. The methods implemented in this project will clarify the properties of this material and may suggest how to design new superconductors. The project will also allow students from a small undergraduate university to accompany the principal investigator to a national laboratory where they will gain computational research skills and further develop their identity as scientists. Technical DescriptionMonolayer FeSe on SrTiO3 has been actively studied since the discovery of its enhanced superconducting temperature Tc of 60 – 80 K, compared to around 8 K in bulk FeSe. Theoretical investigations have focused on a pure FeSe / SrTiO3 interface, but atomic-resolution scanning transmission electron microscope (STEM) images have revealed the existence of an additional titanium-oxide layer between the SrTiO3 substrate and FeSe. The P.I. recently published computational results that demonstrate that this layer exhibits a titanium excess that can participate in electron-doping the FeSe monolayer. This doping is thought to be important in increasing Tc in this system. While these density functional theory results provide a good description of the atomic structure of this material, there are technical and fundamental limits to such methods’ ability to accurately describe a realistic heterostructure. After extracting material-specific model parameters from these calculations, the P.I. will perform more sophisticated calculations that will clarify which of the properties of the system are most important to the superconducting state. The effect of disorder or different ordering in the extra interfacial layer will be explored by constructing multiple structural configurations and averaging over their band structures. Further, surface Green functions will be computed to determine the electronic structure of the monolayer and interfacial layer on a more realistic semi-infinite substrate. Such results can also provide insight into how similar increases in Tc might be engineered in other materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

无损耗传输电力的承诺使得标准温度和压力下的超导性成为材料科学中最诱人的目标之一。然而，要找到一条前进的道路，科学家们必须研究单个材料。了解它们的工作原理以及它们的共同点。该项目将为研究超导材料如何对其原子结构的变化做出反应提供计算工具，从而使研究人员能够预测提高超导材料工作温度的方法。超导材料，使实验能够集中在最有希望的候选材料上，这些工具将应用于沉积在钛酸锶（SrTiO3）上的硒化铁（FeSe）的情况，在 SrTiO3 上生长的单个三原子厚的 FeSe 层仍然具有超导性。温度几乎是较大的纯 FeSe 晶体的 10 倍。该项目中采用的方法将阐明这种材料的特性，并可能建议如何设计新的材料。该项目还将允许一所小型本科大学的学生陪同首席研究员前往国家实验室，在那里他们将获得计算研究技能并进一步发展他们作为科学家的身份。其增强的超导温度 Tc 为 60 – 80 K，而块状 FeSe 的超导温度约为 8 K。理论研究主要集中在纯 FeSe / SrTiO3 界面，但具有原子分辨率扫描传输。电子显微镜 (STEM) 图像揭示了 SrTiO3 基底和 FeSe 之间存在额外的氧化钛层。P.I. 最近发表的计算结果表明，该层表现出过量的钛，可以参与 FeSe 单层的电子掺杂。这种掺杂被认为对于增加该系统中的 Tc 很重要，虽然这些密度泛函理论结果很好地描述了该材料的原子结构，但此类方法准确描述实际情况的能力存在技术和基本限制。从这些计算中提取特定材料的模型参数后，P.I. 将执行更复杂的计算，以阐明系统的哪些特性对超导状态最重要。将通过构建多个结构配置并对其能带结构进行平均来进行探索，此外，还将计算表面格林函数以确定更真实的半无限衬底上的单层和界面层的电子结构。深入了解如何在其他材料中设计类似的 Tc 增加。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。